In the past, surface safety valves have had valve actuators. These valve actuators have been hydraulically operated, having a failsafe feature to close the valves upon failure of hydraulic pressure to the actuator. Typical of such actuators are Baker Oil Tools Model CSWC, which is a coiled spring wire cutter typically used for failsafe shut applications during extended wireline operations. Such actuators are used for operating pressures as high as 15,000 psi, with 6000 psi controlled pressure. This actuator can also accommodate 10,000 psi controlled pressures. Other types of hydraulic actuators, having a failsafe operation, are also known. Typical of such actuators are those made by Otis under Model Nos. UDUH or WC. Axelson makes a type HC actuator. Generally, the hydraulic or pneumatic designs have incorporated a feature which, depending on the needs of the application, automatically opens or closes In an emergency situation such as the loss of motive fluid pressure.
Electrically actuated valves have not been in use in surface safety valve applications because of difficulties in providing a failsafe feature In the event of loss of electrical power. Yet, in some applications, it is more convenient for the operator to use electrically actuated surface safety valves than to use pneumatic or hydraulically operated valves. In some instances, regulations may require storage of significant quantities of hydraulic fluid in reserve in a location where space is at a premium, such as an offshore platform. In that situation, using an electric drive is more efficient. Additionally, a drive that uses an electric motor is generally simpler to install and costs less than a more complicated hydraulic system. Accordingly, one of the objects of the present invention is to provide an actuator that can be operated using an electric motor input while still providing a failsafe feature.